The present invention relates to a system for selectively applying either heat or cold to a local area, and particularly when it is desired that the temperature of the applicator be held substantially constant. The present invention is useful in many areas, principally in the medical field. One of the advantages of the present system is that, depending upon the applicator pad which is attached to the system, the applicator may be used as a conventional external applicator, or it may be used during surgery to apply to incisions or open wounds, or it may be used to rapidly cool or re-heat an organ during transplant, etc.
The present invention is preferably used with an applicator pad of the type disclosed in co-owned U.S. patent application Ser. No. 381,733, of Francis C. Moore and Leon R. Perkinson, for "Disposable, Sterile Temperature Control Applicator Pad for Medical Application", filed July 23, 1973.
Heat applicators have long been used in the medical field, and they frequently take the form of a padded or blanket type of applicator provided with internal resistive wiring for generating heat. Probably the most commonly used type of cold applicator in the medical field is a flexible plastic package containing two chemicals which, when mixed absorb heat. The chemicals are packaged on either side of a rupturable membrane so that the application of pressure to the exterior of the package ruptures the membrane and causes the fluids to mix and producing the heat-absorbing reaction. Another type of cold applicator uses a compressor, refrigerant, condensing and evaporator coils, and a permanent or non-disposable applicator. Such units are heavy and cumbersome.
The present invention uses a heat transferring liquid stored in a reservoir, such as a standpipe, which is pumped by a peristaltic pump through a heat exchanger containing thermoelectric diodes. As is known, if a current is forced in one direction (anode to cathode) through a thermoelectric diode, the diode will produce heat through ohmic losses. If a voltage of opposite polarity is applied to the junctions of the diode, then the diode will absorb heat from its surrounding area. Control circuitry, under control of an operator, determines which polarity of electrical potential is applied to the thermoelectric diodes in the heat exchanger, and in either case the applied voltage is a rectified sine wave. The control circuitry also determines the firing angle at which the applied voltage is coupled to the thermoelectric diodes, and this firing angle is adjustable. Hence, the operator, in addition to determining whether the system will supply heat to the transfer liquid or absorb heat from the transfer liquid, may adjust the temperature of the transfer liquid in either the hot or cold region. A temperature-sensitive transducer is associated with the passageway from the transfer liquid reservoir and included in the electronic control circuitry in such a way as to regulate the temperature of the transfer liquid once a setting has been made by the operator.
Another feature of the invention is that a second subsystem of reservoir, heat exchanger and pump may be used, connecting the shaft of the second peristaltic pump in tandem with the shaft of the first so that they are driven by a single motor. In this system, the second fluid system may be used, for example, to flush a transplant organ with saline solution at a controlled temperature, either hot or cold or successively cold and hot. Thus, great flexibility in usage is provided. In the case of one heat transferring liquid system, it is preferred that the total liquid in the system, including reservoir, heat exchanger and tubing be less than about two quarts, and the liquid may be water. This permits a very rapid response in the applicator pad to changes in temperature setting. Further, the present system provides greater conduction of heat to or from the application surface because it permits the use of a wet applicator pad. Such pad, as disclosed in the above-identified application further permits the application of medicaments or sterilizing agents to the application area.
Other features and advantages of the present will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing.